The present invention relates generally to internal combustion engines for automotive vehicles, and more particularly to crankshaft assemblies integrated within variable displacement internal combustion engines (VDIC engines) of automotive vehicles.
Variable displacement internal combustion engines (VDIC engines) are known for improving fuel economy by reducing the amount of functioning displacement when vehicles require less power. The amount of functioning displacement is typically reduced by disabling the valves associated with at least one cylinder.
For example, a vehicle having an eight cylinder VDIC engine may derive sufficient power for idle operation conditions from four of its cylinders. The VDIC engine may disable valves associated with four of its cylinders. The reduction in functional displacement consequently reduces the power supplied by the engine, so that to maintain the same idle speed in the four-cylinder mode that the engine had in the eight-cylinder mode, the absolute pressure in the intake manifold is increased. The corresponding decrease in the pressure drop across the throttle plate results in an improvement in the engine""s operating efficiency. The engine may be quickly returned to eight-cylinder operation, when the accelerator is pressed to the floor for maximum acceleration. Thus, the VDIC engine improves fuel economy without sacrificing needed power.
FIG. 1 is a graphic illustration of a typical crankshaft torque output of an eight-cylinder, four-stroke VDIC engine operating during a full displacement mode 10 and a reduced displacement mode 12.
A reduced displacement operation curve 12 represents torque experienced by a crankshaft of the VDIC engine during a reduced displacement operation. For instance, in reduced displacement operation of the eight-cylinder engine the valves associated with four of the cylinders are deactivated. By disabling some of the cylinders, one skilled in the art would understand that the frequency of torque pulses is likewise reduced. The magnitude of the torque pulses during reduced displacement operation is necessarily higher than the magnitude of the torque pulses during full displacement operation to provide approximately equal mean torque output.
The increased magnitude and decreased frequency of torque pulses during reduced displacement operation typically result in unacceptable noise, vibration, and harshness (NVH) levels within the vehicle. In general, NVH levels are within an acceptable range during full displacement operation of the VDIC engine because vehicular components are tuned for optimal function at a torque pulse frequency of the crankshaft at full displacement. For example, the stiffness of engine mounts, seats, steering columns, and floor pans are typically tuned to minimize the NVH excited by the fourth order crankshaft torsional vibration generated by the full displacement operation of eight-cylinder engines. Further, vehicular components normally have natural frequencies less than the torque pulse frequency provided at full displacement operation. However, during reduced displacement operation, the torque pulses increase in magnitude and sufficiently decrease in frequency thereby exciting the natural frequencies of some vehicular components. As a result, NVH levels may rise to unacceptable levels within the vehicle. Such a result is clearly undesirable.
Some airplane piston engines use pendulum vibration absorbers to smooth mean torque output of their crankshafts and reduce stress within the crankshaft and in the drivetrain to the rotating airfoils. These vibrations result from torque pulses exerted by the piston and connecting rod assemblies on the crankshaft. The magnitude of the torsional vibrations is the fluctuation between the maximum torque output and the minimum torque output of the crankshaft. The inertia of the vibration absorbers reduces the maximum torque output and increases the minimum torque output thereby decreasing torsional fluctuations.
Furthermore, most V6, V8, and V10 engines have an inherent first order unbalanced couple that rotates the same direction as the crankshaft. It is common practice to construct the crankshafts of these engines with a large counterweight near the front of the crankshaft, and another large counterweight, diagonally opposite, near the rear end of the crankshaft. The combination of these counterweights generates the appropriate first order couple to cancel the engine""s inherent first order unbalanced couple caused by the accelerations of reciprocating masses along the axes of the engine""s cylinder bores. Regarding aircraft engines that have pendulum vibration absorbers, typically two vibration absorbers of equal mass are coupled to the crankshaft in the same rotational plane and 180 degrees from each other. As one absorber thrusts upward, the other absorber thrusts downward. In this regard, the pendulum vibration absorbers are balanced on the crankshaft so as to cancel each other""s first order balancing forces. Therefore, current pendulum vibration absorbers fail to generate the couple needed to provide first order engine balance.
Moreover, the pendulum vibration absorbers require several parts for attaching to the crankshaft. These parts include pins, bushings, thrust plates, and snap rings. The bushings are fabricated from high strength, wear resistant material for reducing wear between surfaces of the pendulum vibration absorber and the pin. The thrust plate prevents the pin from sliding out of the bushing. Furthermore, the snap ring holds the thrust plate in its position. The incorporation of these several parts increases manufacturing cycle time and costs.
Flywheels also smooth the mean torque output of crankshafts. As one skilled in the art would understand, a conventional flywheel is fixedly engaged to one end of a crankshaft. The inertia of the flywheel opposes torsional fluctuations of the crankshaft. The greater the moment of inertia of the flywheel, the smaller the torsional vibration of the crankshaft. Typically, the inertia of the flywheel may be increased by increasing the size of the flywheel. However, the increased inertia and physical size of the flywheel also typically result in sluggish engine and vehicle acceleration, diminished fuel efficiency, and decreased available space within the vehicle.
The inventors of the present invention have recognized that a need exists to reduce vibrations caused by torsional crankshaft vibrations and first order unbalanced couples within a VDIC engine of an automotive vehicle without sacrificing fuel efficiency and with minimal increase to complexity.
The present invention reduces vibrations caused by torsional crankshaft fluctuations and first order unbalanced couples in a variable displacement internal combustion engine (VDIC engine) of an automotive vehicle.
In carrying out the present invention, a crankshaft passively reduces vibrations to an acceptable range for permitting the operation of the VDIC engine at reduced displacements.
There is disclosed herein a crankshaft assembly for a VDIC engine of an automotive vehicle. The crankshaft assembly includes a crankshaft integrated within an internal combustion engine. The crankshaft has a first portion with a first pendulum vibration absorber assembly integrated therein and a second portion with a second pendulum vibration assembly absorber integrated therein. The first portion is offset from the second portion along an axis of the crankshaft. Each absorber assembly includes a counterweight member integrally formed within the crankshaft. The counterweight members have a desired counterweight mass that contributes to first order engine balance. Furthermore, each counterweight member has a pendulum vibration absorber pivotally coupled thereto. The pendulum vibration absorbers have a desired mass and geometry for providing a torsional vibration cancellation as well as first order engine balance.
Two advantages of the present invention are the reduction of vibrations caused by torsional fluctuations and the balance of the inherent first order couple within a VDIC engine of a vehicle. Another advantage of the present invention is that the vibrations are reduced passively without the need for complex timing mechanisms and additional drive shafts. Yet another advantage of the present invention is the efficient use of space within the VDIC engine. Still another advantage of the present invention is the reduction of couplings used to fasten the pendulum vibration absorber to the counterweight member. Yet another advantage of the present invention is that because vibration during less than full cylinder operation is reduced, the operating range over which less than full cylinder operation can be used, without excessive NVH, is increased. By increasing the range over which less than full cylinder operation can be employed leads to an increase in fuel efficiency.
Other advantages of the present invention will become apparent when viewed in light of the detailed description of the preferred embodiment when taken in conjunction with the attached drawings and appended claims.